The present invention generally relates to contact lenses and more specifically relates to contact lenses having microchannels that promote effective tear fluid exchange.
It has long been recognized that extended wear of contact lenses can lead to corneal complications. Adverse corneal responses to extended contact lens wear are believed to be primarily caused by accumulation of debris trapped at the lens-eye interface.
The cornea is a living tissue with an active metabolism. Waste products, for example lactic acid, carbon dioxide and water, generated by such metabolism must be expelled from the cornea. Contact lens wear results in debris, for example, derived from such waste products, dead epithelial cells, and other materials which are ordinarily removed from the eye, becoming trapped at the lens-eye interface. Such debris, if left to accumulate in the eye, can harm the eye, for example, causing irritation and/or other harm to the eye and/or to the general ocular health of the lens wearer. In order to remain healthy, the cornea must receive an adequate supply of oxygen as the cornea does not receive oxygen from the blood supply as does other living tissue. If sufficient oxygen does not reach the cornea, corneal swelling occurs.
In order to address the problem of oxygen deprivation due to extended wear of contact lenses, hydrophilic lenses with high oxygen transmission properties were developed. Hydrophilic lenses, also sometimes referred to as hydrogel lenses, are soft, flexible, water-containing lenses. Clinical studies of hydrophilic lenses have indeed shown a relatively lower degree of corneal swelling in persons wearing such lenses, even when worn over an extended time.
Unfortunately, however, the use of conventional hydrophilic lenses have not eliminated all adverse corneal responses to contact lens wear, in particular extended contact lens wear. For example, conventional hydrophilic lenses do not address the problem of debris accumulation at the lens-eye interface. This suggests that in addition to oxygen permeability, there are other considerations to be addressed in the development of a safe, soft contact lens for extended wear.
One important consideration is effective tear film exchange between the exposed surface of the eye and the surface of the eye covered by the lens. Tear fluids provide for hydration of delicate eye tissue and continuous flushing of debris from the eye. Tear film exchange between the eye and the posterior, i.e. eye facing, surface of a contact lens, is believed to be a critical factor in maintaining eye health. Tear film exchange allows for removal of dead epithelial cells, foreign particulate matter and other debris that may otherwise become trapped between the lens and the eye. It has been hypothesized that increased tear film exchange will not only enhance corneal health but will limit complications such as infection in the eye and microbial keratitis.
Rotation of the lens on the eye has long been recognized as a means of maintaining eye health and comfort. For example, Gordon U.S. Pat. No. 2,989,894 describes a contact lens having five equally spaced, spirally inclined ducts formed on an inner surface of the lens. Each duct is described and shown as extending toward a center of the lens but without extending as far as the corneal region. It is stated that the slow and constant rotation of the lens prevents excess settling of the lens on the cornea. The spiral inclination of the ducts is said to cause the lens to rotate in a clockwise or counterclockwise direction depending upon the direction of inclination.
More recently, Höfer et al U.S. Pat. No. 5,166,710 discloses a contact lens having a corneal region that, when placed on the eye, is spaced apart from the corneal surface. Provision is made for causing the lens to rotate upon eyelid blinking action of the wearer. According to Höfer et al, lacrimal film is transported along the eye surface as a result of a “turbo effect” produced by flattened zones on the lens, which causes the lens to rotate on the eye in response to blinking action. The patent also describes that tear transport may be provided by depressions in the rear face of the lens body. Höfer et al shows and describes that the depressions may be depressed portions of the lens body, within the rear surface thereof, the depressions being groove-like or saw tooth-like in shape. Höfer et al describes that it is also possible to provide “thin wave-like curved channels”.
Nicolson et al U.S. Pat. No. 5,849,811 discloses a lens material that was developed to provide a balance of oxygen permeability with ion or water permeability, with the permeability being sufficient to provide contact lens “eye-on movement”, i.e. movement of the lens on the eye surface.
The disclosure of each of the patents identified herein is hereby incorporated in its entirety herein by this specific reference.
Despite the advances made in development of comfortable, safe, extended wear contact lenses, there is still a need for an improved contact lens, for example, a lens that promotes effective tear fluid exchange throughout the surface area of the eye, particularly in the area of the cornea.